1. Field of the Invention
This invention relates to apparatus for the printing and labelling industry, and in particular relates to a new butt cutting apparatus for use with rotary presses.
2. Description of the Prior Art
Rotary butt cutters are widely used in the printing and label stock industry in connection with label stock that is supplied with pressure sensitive adhesive and is attached to a releasable liner. Butt cutters are used to cut through label stock without cutting through the releasable liner attached to such material. This task requires high precision as only slightly improper cut depth results in either the labels not separating from the matrix, or in the label separating from the matrix but remaining affixed to the liner. Either scenario will typically cause malfunctioning of most automatic labelling machines.
There are two main types of apparatus currently used for butt cutting. The most common type of equipment makes use of two cooperating rollers or anvils, one of which is the cutting anvil and the other is a roller anvil against which the cutting anvil bears as the stock is cut. The cutting anvil is provided as an engraved die. These engraved dies do offer the high degree of precision required in the butt cutting operation. The use of engraved dies however is extremely expensive as a different die is required for each configuration and size of label stock to be cut. This requires that a substantial investment in tooling be made as several different dies must b=kept available for different tasks. The dies are also susceptible to damage and wear. If even one cutting edge of the die is damaged the entire die must be discarded. In normal conditions a die will also wear and become dull and must be sharpened. Typically, a die can be sharpened two or three times and then it must be discarded. Thus, while providing the required degree of accuracy for the butt cutting process, engraved dies as a cutting means are extremely expensive as an initial investment and as an ongoing expense.
The other type of standard equipment used for butt cutting operations also employs two cooperating anvils, one as a cutting anvil and the other as a bearer anvil. The main difference in this type of equipment is that the cutting apparatus is not permanently affixed to the anvil as with the engraved dies, but is provided by blades which are removably secured onto the cutting anvil. Most typically, this type of equipment is standard sheeting (cutting) or perforating equipment which is adapted to be used for the butt cutting operation. Although most manufacturers of sheeting or perforating equipment do not recommend it for butt cutting purposes as it typically cannot generate the required precision, it is often used because it is much less expensive than having separate engraved dies for each different configuration of material that is to be cut. The cutting edge of the blades and the surface of the cooperating anvil normally rotate at the same speed, and the stock is cut as the blades move in and out of engagement with the anvil surface. It is desired that the stock be cut as cleanly and accurately as possible. In typical machines, there is a need to replace blades frequently as any blade damage or significant blade wear will result in improper depth cuts resulting in the label stock not being cut through or in the label stock and the backing both being cut through. As such, a substantial amount of time is spent replacing worn or damaged blades.
In conventional rotary butt cutting apparatus utilizing replaceable blades, blade replacement is a very time consuming operation. The blades are set into slots or grooves which are milled into the surface of the cutting anvil. The blades are secured into position in the grooves by an appropriate securing means, typically being set screws. As it is virtually impossible to machine the grooves in the anvil to the required precision, it is necessary to "shim" the blades to achieve correct depth adjustment. When changing a blade the new blade is again loosely set into place and the anvil rotated so that the precise depth adjustment can be made. Once the correct height of the blade has been determined the height of the blade is then maintained by placing the shims under the blade. The blade is then tightened into its final cutting position. As stated, these procedures are very time consuming and result in considerable down time for the presses.
The present invention is directed to overcoming these and other difficulties inherent in the prior art. In the present invention a cutting anvil is provided with a removable cutting apparatus, which does not contain grooves into which the blades are secured. The present invention utilizes a cutting anvil which has a precision ground outer diameter against which the blades are secured by means of block assemblies. The height of each blade is ensured to be identical by having the blades precision ground to the same height prior to their installation onto the cutting anvil. Blade replacement can therefore be accomplished in a much shorter time than in conventional apparatus, as the new blades are simply set against the cutting anvil and immediately secured into place. This results in less set up time in adjusting blade heights and accordingly in less down time in production.
The use of a removable cutting apparatus also eliminates the need to maintain an expensive set of engraved dies.